The present invention is generally directed to a serial data communication system and, in particular, to a circuit for power transmission and serial data communication which transmits both power and data through two balanced transmission lines connecting a main controller and a sub-station separated by a distance. Most of the previous serial data communication systems were configured with separate power transmission and data transmission paths. This required a significant number of connection lines to link a main controller to a sub-station. Also, to improve the reliability of data communication the data transmission circuits were configured as a balanced network, which required additional complexity.
Accordingly, a power transmission and data communication circuit which transmits power from the main controller to a sub-station through two transmission lines and also, at the same time, transmits data along the same two transmission lines, all in a balanced network, is desired. It is also desired to extend the range between the main controller and one or more remote sub-stations without significant power loss or susceptability to outside interference.